In addendum to these comments on Technology: ups and downs:
Wars seem to have decreased. But more likely they are spread out over a larger area and contained as smaller, localized wars and will limit the larger massive death counts. …
And wars are about resources.
A new government-commissioned report on the looming climate-induced food shortage suggests that “the rise of Isis may owe much to the food crises that spawned the Arab spring”.
In his book, Collapse: How Societies Choose to Fail or Succeed, Jared Diamond points out that the most environmentally stressed places in the world are the most likely to have conflicts, which then generate refugees. Rapid climate change will environmentally stress lots of developing countries.
Check out this graph again. Look at the increasing cluster of small conflicts after the Second World War.